1. Field of the Invention
The present invention relates generally to an apparatus for operating a discharge lamp, and more particularly, to an apparatus for reducing the chances that a person working on the lamp will receive an electrical shock.
2. Description of the Related Art
Many kinds of apparatus have been known for operating a discharge lamp with high frequency power. They are classified into two types. One type of apparatus uses an insulating transformer which insulates the input side from the output side. The other type does not use an insulating transformer and is called the "directly-connected power source" type.
The former type is usually effective in preventing a person who changes a lamp from receiving an electrical shock, even if the lamp is connected with a socket only at one side. However, it is generally a disadvantage that the insulating transformer is too large.
The directly connected power source type apparatus is smaller than the insulating transformer, but it is not as effective in preventing a person who changes a lamp from receiving an electrical shock when a lamp is connected with a socket only at one end. Such a directly connected apparatus permits a leakage current to flow through a floating capacitance to the person.
In order to reduce the likelihood of electrical shock, sensing means have been provided at both ends of the lamp for sensing the connection between the lamp and the apparatus and means for supplying high frequency power to the lamp becomes operative only when the lamp is connected with the apparatus at both ends of the lamp. However, regardless of whether the sensing means electrically senses current or voltage, or whether it senses mechanically, two sensing means are required to sense connections at both ends of the lamp, and therefore the sensing means is complex and expensive.